Programmed cell death mechanisms of identifiable peptidergic neurons inDrosophila melanogaster

Abstract

The molecular basis of programmed cell death (PCD) of neurons during early metamorphic development of the central nervous system (CNS) in Drosophila melanogaster are largely unknown, in part owing to the lack of appropriate model systems. Here, we provide evidence showing that a group of neurons (vCrz) that express neuropeptide Corazonin (Crz) gene in the ventral nerve cord of the larval CNS undergo programmed death within 6 hours of the onset of metamorphosis. The death was prevented by targeted expression of caspase inhibitor p35, suggesting that these larval neurons are eliminated via a caspase-dependent pathway. Genetic and transgenic disruptions of ecdysone signal transduction involving ecdysone receptor-B (EcR-B) isoforms suppressed vCrz death, whereas transgenic re-introduction of either EcR-B1 or EcR-B2 isoform into the EcR-B-null mutant resumed normal death. Expression of reaper in vCrz neurons and suppression of vCrz-cell death in a reaper-null mutant suggest that reaper functions are required for the death, while no apparent role was found for hid or grim as a death promoter. Our data further suggest that diap1 does not play a role as a central regulator of the PCD of vCrz neurons. Significant delay of vCrz-cell death was observed in mutants that lack dronc or dark functions, indicating that formation of an apoptosome is necessary, but not sufficient, for timely execution of the death. These results suggest that activated ecdysone signaling determines precise developmental timing of the neuronal degeneration during early metamorphosis, and that subsequent reaper-mediated caspase activation occurs through a novel DIAP1-independent pathway.

Ecdysone-mediated programmed cell death in Drosophila

“…A second pulse of ecdysone approximately 12 hours after puparium formation (h APF) signals the transition from prepupal to pupal development and initiates PCD of the larval salivary glands (Jiang et al, 1997, Lee et al, 2002b. In addition, ecdysone regulates the PCD of the optic lobe and two distinct groups of neurons in the ventral central nervous system (Choi et al, 2006, Hara et al, 2013, Winbush and Weeks, 2011. Ecdysone-mediated PCD is not only restricted to larval-pupal metamorphosis but also occurs in the adult fly ovary (Pritchett et al, 2009).…”

“…In Drosophila, developmentally timed pulses of the steroid hormone 20-hydroxyecdysone (ecdysone) initiates processes such as molting and larval-pupal metamorphosis (Riddiford et al, 2000, Thummel, 2001. Of these processes, ecdysone induces the histolysis of many obsolete larval tissues during larval-pupal metamorphosis such as the midgut, salivary gland, anterior and abdominal muscles, and distinct subsets of neurons in the nervous system and optic lobe (Choi et al, 2006, Fahrbach et al, 2005, Hara et al, 2013, Jiang et al, 1997, Kumar and Cakouros, 2004, Lee et al, 2002a, Winbush and Weeks, 2011, Zirin et al, 2013. Additionally, ecdysone is important for the remodelling of the fat body and nervous system (Boulanger and Dura, 2014, Kirilly et al, 2009, Kuo et al, 2005, T. , Loncle and Williams, 2012, Rusten et al, 2004, Williams and Truman, 2005.…”

A Drosophila Gain-of-Function Screen for Candidate Genes Involved in Steroid-Dependent Neuroendocrine Cell Remodeling

“…Differentiated larval neurons adopt one of two fates: programmed cell death or morphological remodeling (Truman 1992). The programmed cell death of many larval neurons occurs through autophagy or apoptosis (Weeks 2003;Choi et al 2006). Neuronal remodeling involves the selective elimination of larval neurites and the outgrowth and elaboration of adult-specific projections (Levine and Truman 1982;Lee et al 2000).…”

“…Molting and metamorphosis are coordinated by two families of hormones, the juvenile hormones and the ecdysteroids (Nijhout 1994). During metamorphosis, ecdysteroids act cell autonomously to control neuronal cell fates (Robinow et al 1993;Lee et al 2000;Brown et al 2006) through evolutionarily conserved cellular mechanisms and signaling pathways (Draizen et al 1999;Kinch et al 2003;Watts et al 2003;Choi et al 2006;Hoopfer et al 2006).…”

Characterization of neuronal apoptosis in the ventral ganglia of postembryonic silkworms Bombyx mori (Lepidoptera: Bombycidae)

“…Indeed, the pattern of neuronal apoptosis in the VG of insects during the larval to pupal stages is poorly understood and based on only a few studies on the adult CNS of Drosophila (Truman & Schwartz, 1984;Truman et al, 1993;Karcavich & Doe, 2005;Choi et al, 2006;Rezával et al, 2007;Bass et al, 2007;Kato et al, 2009) . Therefore, fluorescent triple staining by TUNEL assay using the antibody anti-horseradish peroxidase (HRP) conjugated with Cy3, 4',6-diamidino-2-phenylindole (DAPI), and 2'-deoxyuridine 5'-triphosphate (dUTP) conjugated with FITC was used to analyze the pattern of neuronal apoptosis in the twelve VG of the silkworm during the different periods of postembryonic development (Tettamanti & Malagoli, 2008).…”